Effect of preparation method on the structure and properties of coal tar model compound cracking catalyst Ni/Al₂O₃

Cat-1, Cat-2, Cat-3 and Cat-4 catalysts were synthesized via different preparation methods that are incipient wetness, impregnation-precipitation and mechanochemical method (carriers from market and homemade for comparison), and then characterized by BET, H₂-TPR, XRD, XPS and NH₃-TPD. The cracking behavior of toluene and pyrene (3%, mass fraction) (coal tar model compounds) were investigated to evaluate the catalytic performance of the stated catalysts. The catalyst characterization showed that the pore size of all the catalysts belonged to mesoporous range, and Cat-4 catalyst exhibited higher ordered mesoporous and larger surface area than others, up to 235 m²/g. Besides, the peak area of NiAl₂O₄ spinel reached up to the highest value of 85.2%. The dispersion of Ni in the reduced Cat-4 was the highest and its particle size was the lowest value, about 10.0 nm. Which means that there are more active sites. The catalytic performance results showed that the cracking rate of pyrene varied little for other catalysts, except for Cat-1, but the lowest carbon deposition of 10.84% was obtained under the action of Cat-4, while the carbon deposition of Cat-1, Cat-2 and Cat-3 increased by 35.0%, 74.7% and 45.7% respectively compared with that of Cat-4. Thus, Cat-4 prepared by mechanochemical method is more suitable for the cracking of toluene and pyrene system because of highest BET surface area, which is favorable for the dispersion of active component, and at the same time, the highest content of NiAl₂O₄ can inhibit the formation of carbon.